Poly(arylene ether) resin is a type of plastic known for its excellent water resistance, dimensional stability, and inherent flame retardancy. Properties such as strength, stiffness, chemical resistance, and heat resistance can be tailored by blending it with various other plastics in order to meet the requirements of a wide variety of consumer products, for example, plumbing fixtures, electrical boxes, automotive parts, and insulation for wire and cable.
A different plastic, poly(vinyl chloride), is currently the commercially dominant material for flame retardant wire and cable insulation. However, poly(vinyl chloride) is a halogenated material. There is mounting concern over the environmental impact of halogenated materials, and non-halogenated alternatives are being sought. There is therefore a strong desire—and in some places a legislative mandate—to replace poly(vinyl chloride) with non-halogenated polymer compositions.
Recent research has demonstrated that certain halogen-free poly(arylene ether) compositions can possess the physical and flame retardant properties needed for use as wire and cable insulation. See, for example, U.S. Patent Application Publication Nos. US 2006/0106139 A1 and US 2006/0182967 A1 of Kosaka et al. The compositions disclosed in these references can exhibit good flame retardancy and good physical properties such as flexibility and tensile stress at break. Although the poly(arylene ether) component of these compositions is itself relatively flame retardant, substantial amounts of other flame retardants are typically added to assure that the compositions as a whole are sufficiently flame retardant. Trade-offs in physical properties typically accompany the relatively large amounts of flame retardants required. For example, when the flame retardant composition comprises substantial amounts of a metal hydroxide such as magnesium hydroxide, flexibility (as measured, for example, by the objective property tensile elongation) is compromised. As another example, when the flame retardant composition comprises substantial amounts of a liquid organic phosphate flame retardant, the flame retardant can migrate to the surface of the insulation, creating an esthetic problem and, more importantly, compromising the flame retardancy of the composition. There remains a desire for flame retardant poly(arylene ether) compositions that exhibit an improved balance of flame retardancy, physical properties, and esthetic properties.